Storage means for a liquefied gas



y 1962 J. J. HENRY 3,041,841

STORAGE MEANS FOR A LIQUEF'IED GAS Filed June 24, 1958 50 36 FIG J 33 ll H r S 1 6 .24 {T H H 7 6 INVENTOR.

fitter-megs United States Patent @iifice 3,041,841 Patented July 3, 1962 3,041,841 STORAGE MEANS FGR A LIQUEFIED GAS James J. Henry, New York, N.Y., assignor, by mesne assignments, to Conch International Methane Limited, Nassau, Bahamas, a corporation of the Bahamas Filed June 24, 1953, Ser. No. 744,238 1 Claim. (Cl. 62-45) This invention relates to the storage or transportation of a liquefied gas which boils at low temperature and it relates more particularly to controls to prevent the existence of pressure conditions within a container which might otherwise cause breakdown of the container in which the liquefied gas is housed during its storage or transportation.

This invention will be described with reference to the storage and transportation of liquefied natural gas but it will be understood that concepts described will have application to the storage and transportation of other low boiling liquefied gases which have to be retained at extremely low temperatures for maintenance in a liquefied state.

Housing of the liquefied gas in large containers at high pressure is undesirable because of the large amount of metal which would be required in building up walls of suflicient thickness to withstand the load conditions which would be existing. It is much more practical to make use of a container of large capacity which is designed to operate at about atmospheric pressure or preferably slightly above so that the forces required to be with stood by the walls of the container would be comprised chiefly of the head of liquid in the container. At atmospheric pressure, liquefied natural gas, composed mostly of methane, would boil at some temperature starting with -258 F. or slightly above the described boiling point for methane, depending upon the amount of heavier hydrocarbons present in the liquefied natural gas. In general, the boiling point temperature will reside somewhere between about 240 F. and -258 F. for natural gas and somewhat lower in some of the other liquefied gases.

The extremely low boiling point of the liquefied gas leads to a number of problems in construction and operation of the tank. One of the problems stems from the filling of the tank when portions or all of the tank have been allowed to warm up to a temperature considerably above the boiling point temperature of the liquefied gas. When this condition exists, introduction of the liquefied gas at too rapid a rate will result in excessive vaporization of the liquid to cause build-up of pressure within the tank which may exceed the forces capable of being withstood by the tank so as to cause breakdown thereof. Thus, as defined in the companion case filed concurrently herewith, Serial No. 744,141, filed June 24, 1958, now Patent No. 2,966,040 and entitled Tank for the Storage and Transportation of a Low Boiling Liquid, the liquefied gas is introduced into the tank at a rate slow enough to enable the vapors generated to be handled until the tank is cooled down to a level where the liquefied gas can be introduced at a high rate for filling without excessive vaporization. Even then, sometimes the amount of vapor generated is incapable of being handled by the usual vapor removal means and, as a result, build-up of excessive pressures becomes possible.

Further, after proper cool-down has been effected, and the means for handling the large amount of vapor during cool-down has been shut off, filling of the tank at a too rapid rate will cause displacement of the vapors in the tank at a rate greater than calculated with the result that a build-up in pressures may occur which will let loose destructive forces within the tank.

Still further, the storage tank is usually provided with a thick layer of insulating material to minimize heat loss from the ambient atmosphere but even then some heat will naturally migrate from the atmosphere to the liquid content material to cause some vaporization thereof. These vapors can usually be taken care of by suitable means to draw ofi the vapors for use as a fuel or for use as refrigeration or for reliquefaction and return to the storage tank or possibly even for venting vapors off into the atmosphere. Such means, however, are usually not adequate to handle large amounts of vapor which might suddenly he released in the event of failure of the insulation or in the event of an act of God which would enable excessive heat loss to the liquefied gas within the container. As a result, sudden build-up of pressure would occur under the most unfavorable conditions with possible destruction of the tank or container.

Difiiculties will arise not only from the buildup of pressure beyond a safe maximum but corresponding difficulties would also arise upon the development of excessive vacuum conditions within the tank. Such conditions are possible under a number of circumstances. For example, the storage tank on-ship or on land may become stranded for a period of time suficient to vaporize off all of the liquefied gas contained therein to the point where the container is filled only with vapors. Under such circumstance, a drop in ambient temperature will automatically result in a drop in pressure within the tank and, if sufiicient, the drop may be great enough to cause collapse of the tank or parts thereof.

Further, subatmospheric conditions leading to possible collapse could also develop during the unloading of the liquefied gas from the tank when such unloading operations are being carried out at a rate faster than intended. The displacement of liquid from the tank at a rate faster than replacement with another substance will leave vacuum in the tank. If allowed to exist even for a short time, the forces may be sufiicient to cause deterioration of the structure.

Thus it is an object of this invention to produce and to provide a method for producing a safe and eflicient system for the storage of a low boiling liquefied gas.

More specifically, it is an object of this invention to produce a system for the storage and/or transportation of a low boiling liquefied gas wherein use is made of insulated tanks of large capacity embodying means operative automatically to vent the tank when excessive pressures are developed from the vapors generated within the tank and which is operative automatically to feed an inert gas into the tank responsive to the development of subatmospheric pressures beyond a safe maximum and it is a related object to make use of a common system for use in effecting they described operations.

These and other objects and advantages of this invention will hereinafter appear and for purposes of illustration, but not of limitation, an embodiment of the invention is shown in the accompanying drawing in which FIG. 1 is a schematic top plan view of an assembly embodying the features of this invention, and

FIG. 2 is a sectional elevational view of an insulated tank for the storage of a liquefied natural gas.

Referring now to the drawing, the numeral 10 represents an aluminum tank of large capacity formed of a bottom wall 12, side walls 14 and a top wall 16 lined all around with a thick layer 18 of a thermal insulating material. One or more such tanks are arranged in side by side relation for communication with a liquid header 2% for the passage of liquefied gas therethreugh into the tank for filling and out of the tank for emptying; a vapor header 22 for the removal of vapors from the tank, and

gas.

a relief header 24 for the relief of vapors in the event of the presence of vapors in the tank in an amount in excess of that capable of being properly handled by the vapor header 22 whereby a pressure is developed. Vapor header 22 can also be used for introduction of gas into the tank in the event of the existence of a 'vacuum beyond a predetermined maximum within the tank.

The main liquid header 20 is connected with shore facilities in the event that the tanks are mounted on-ship or, in the event of land storage, the header will be connected to sources of supply or use of the liquefied natural The header 20 is connected by a trunk line 26 to a downpipe 28 which extends in fitting relation through an opening in the top wall of the tank to a point adjacent the bottom in the interior of the tank. A line 30 branches off the trunk line to a pipe which extends downwardly in fitting relation through an opening in the top Wall of the tank for communication with a plurality of spray pipes or spray heads 32. which are arranged to spray liquid onto the walls of the tank to elfect cooldown. Both the trunk line 26 and the branch line 30 are provided with valve members 34 and 36 for controlling the flow of liquid from the header into the tank either through the spray heads for precooling or through the downpipe for filling. A similar downpipe with a pump is used for discharging the tank.

The vapor header 22 can be connected by various means for use or reliquefaction of thevapors or for release of the vapors into the atmosphere. When the liquefied gas is natural gas, the vapor from the header 22 can be used for the generation of power for driving the transportation means or other equipment. The refi'igeration in the vapors can be recovered for cooling various other gases, liquids or materials passed in heat exchange therewith prior to use of the vapors as a fuel or as a raw material. The vapor can also be utilized as a raw material in the petrochemical industry, preferably after its refrigeration has been recovered.

The vapor header 22 is connected by the branch line 38 to a vent opening 40 in the top wall of the tank for the removal of vapors which collect above the level of the liquid 42. A valve 44 is provided in the branch line for control of the flow of vapors therethrough and means are also provided to determine the rate of flow in the vapors whereby vapor flow rate can be employed as a means for detecting the development of conditions causing increased vaporization so that suitable steps can be taken to forestall the occurrence of dangerous conditions. The recording means is illustrated in the drawing as a calibrated orifice 46 arranged in the branch line and connected to a flow meter 48 operatively connected to a flow recorder 50.

The relief header 24 may connect to shore facilities or land facilities but the relief header will usually be connected to a suitable blow-01f a safe distance from the storage facility since the header will be in operation for the transmission of vapors only on such occasions as result from a sudden or unexpected boil-off of a large amount of the liquefied gas at a rapid rate.: Such conditions can be developed in the event of failure of the insulation or the like or because of some act of God or other emergency.

One and preferably more than one branch line, such as the two branch lines 52 and 54 illustrated, connect the relief header 24 with a common line 56 which extends in sealing relation from a vent opening 58 in the top of the tank. Each branch line is provided with a pressure responsive valve 60 which is normally closed but which is set to open in response to positive pressures in the line 56 beyond a predetermined level or in response to vacuum or subatmospheric pressures below a predetermined level. When the valves are opened in response to excessive pressure or excessive vacuum, communication is established with the branch lines 52 and 54.

To relieve subatmospheric conditions in the tank, there is provided a source of supply 64 of an inert gas such as carbon dioxide, nitrogen or the like. The source is connected by line 62 to the vapor relief lines 52 and/or 54. Valve members 66, which are provided in the line, are adapted normally to be closed except when the vacuum conditions are caused to exist in the line 52 or 54 in response to the opening of the pressure valves 60 when a vacuum below the predetermined level exists. Opening of the valve member 66 will allow the inert gas to fiow into the branch line 52 or 54 and to be drawn into the tank to relieve the existing vacuum condition.

It will be apparent from the foregoing that means are provided in combination with a storage tank for a low boiling liquefied gas wherein full control is maintained of the pressures within the tank by automatic operation of elements to relieve excessive pressures within the tank or to introduce vapors or gases into the tank for the relief of a vacuum condition. Such means adapted automatically to operate under a predetermined set of conditions enables safe and efiicient usage of the tank for the storage or transportation of a low boiling liquefied gas in large volume over extended periods of time.

It will be apparent that changes may be made in the details of construction, arrangement and operation, Without departing from the spirit of the invention, especially as defined in the following claim.

I claim:

In the storage of a low boiling liquefied gas which needs to be maintained at'an extremely low temperature for maintaining the material in a liquefied state comprising an insulated storage tank of large capacity, a liquid header, an inlet in communication with the tank through which liquefied gas is introduced into and withdrawn from the tank, and means communicating the liquid header with the inlet for passage of liquefied gas into and out of the tank for filling and emptying, respectively; a vapor header, a vapor outlet in communication with the interior of the tank in the upper portion thereof for venting vapors from the tank, and means communicating the vapor outlet with the vapor. header for the removal of vapors that are formed; a relief header, a relief outlet in communication with the interior of the tank in the upper portion thereof, means communicating the relief outlet with the relief header, pressure responsive means operative normally to close the connecting means between the relief header and the relief outlet to prevent passage of vapor therethrough but which is rendered inoperative to permit passage of vapors responsive to the existence of positive pressures within the'tank beyond a predetermined maximum and subatmospheric pressures within the tank beyond a predetermined minimum; a source of supply of inert gas, a passage communicating the supply of inert gas with the means communicating the relief outlet with the relief header, and pressure responsive means operative normally to close the inert gas passage to block the flow of gases therethrough but which is rendered inoperative to permit passage of inert gas therethrough responsive to the existence of subatmospheric pressures beyond a predetermined minimum within the tank.

References Cited in the file of this patent UNITED STATES PATENTS 1,671,492 Skinner May 29, 1928 2,153,555 Gallery Apr. ll, 1939 2,525,570 Williamson Oct. 10, 1950 2,538,664 Benz Ian. 16, 1951 2,860,815 Finn et al. Nov. 18, 1958 

